The present invention relates to a vibration control device having a solid-state actuator and its driving method, which can be used in an active vibration-eliminating device for actively eliminating environmental vibration of a floor, etc. from precision equipment and a microvibration applying device for carrying out a simulating operation on a microvibration environment and for measuring the microvibration sensitivity of a device.
In recent years, solid-state actuators, such as piezo-elements and magnetostrictive elements, have been used in various fields, such as vibration controlling operations for vibration protection and vibration elimination and vibration generating operations. However, these solid-state actuators have a relatively small displacement when used independently, with the result that in most cases, they fail to achieve a desired object. For this reason, the application of a vibration control device in which a displacement enlarging mechanism using a large-diameter piston and a small-diameter piston with a gap filled with liquid and a solid-state actuator are combined has been proposed (for example, see Japanese Unexamined Patent Publication No. 301354/1995 (Hei 7-301354)). Such a vibration control device using combined displacement enlarging mechanism and solid-state actuator makes it possible to enlarge the displacement of the solid-state actuator in accordance with the ratio of areas of the large-diameter piston and the small-diameter piston, and consequently to obtain the corresponding output from the small-diameter piston side.
The above-mentioned vibration control device having the displacement enlarging mechanism and the solid-state actuator is superior in the vibration-blocking performance (active vibration blocking performance) in low frequency bands at the time when an active controlling operation is carried out while the solid-state actuator is being driven. However, since the active controlling operation potentially possesses the possibility of generating vibration, it is difficult to apply the active controlling operation to vibration control at high frequency bands. Therefore, at high frequency bands, it is preferable to carry out the vibration controlling operation by effectively utilizing a natural vibration-blocking characteristic (passive vibration-blocking characteristic) that the vibration control device itself possesses. However, the above-mentioned vibration control device having the displacement enlarging mechanism and the solid-state actuator has a comparatively high natural frequency, and fails to provide a sufficient passive vibration-blocking characteristic at high frequency bands. Moreover, there have been ever-increasing demands for small-size vibration control devices having solid-state actuators.
Here, the above-mentioned vibration control device having the displacement enlarging mechanism and the solid-state actuator fails to generate a great output displacement since the displacement of the solid-state actuator is small and since it is difficult to provide a great difference in the areas of the large-diameter piston and the small-diameter piston. For this reason, the above-mentioned vibration control device cannot be applied to operations, such as position control and attitude control, in which, in particular, a greater displacement is required. Moreover, in the above-mentioned vibration control device, in the case when a control target member is comparatively soft (in particular, when the rigidity of the supporting system supporting the actuator and the control target member is not sufficient), it is sometimes difficult to carry out an appropriate controlling operation on the control target member since the displacement is absorbed by the deformation of the control target member.
Moreover, the above-mentioned Japanese Unexamined Patent Publication No. 301354/1995 (Hei 7-301354)) does not clearly describe about a means for carrying out the vibration controlling operation with multiple-dimensional, multiple degrees of freedom in the vibration control device having the displacement enlarging mechanism and the solid-state actuator.
The main object of the present invention is to provide a vibration control device and a driving method suitable for such a device, which has a comparatively small size, and has a low natural frequency so that it exerts a superior passive vibration-blocking performance at high frequency bands, while maintaining a superior active vibration-blocking performance at low frequency bands.
Moreover, another object of the present invention is to provide a vibration control device and a driving method suitable for such a device, which can generate a comparatively great output displacement.
Still another object of the present invention is to provide a vibration control device and a driving method suitable for such a device, which has a low natural frequency so that it exerts a superior passive vibration-blocking performance at high frequency bands, while maintaining a superior active vibration-blocking performance at low frequency bands, and also carries out the vibration controlling operation with multiple-dimensional, multiple degrees of freedom.
In order to achieve one of the above-mentioned objects, a vibration control device in accordance with one aspect of the present invention is provided with: a displacement enlarging mechanism having first and second movable sections that are arranged so that a displacement inputted to the first movable section is enlarged and taken out from the second movable section; a solid-state actuator that is placed on a side opposite to the second movable section with respect to the first movable section, and is allowed to shift in a direction so as to move the first movable section of the displacement enlarging mechanism based upon an electric signal supplied thereto; and an inside elastic member that is placed between the second movable section and the solid-state actuator in series therewith.
In this vibration control device, a solid-state actuator is placed on the first movable section side of the displacement enlarging mechanism which enlarges the displacement inputted to the first movable section, and outputs the resulting displacement from the second movable section. The application of such a displacement enlarging mechanism makes it possible to enlarge the displacement of the solid-state actuator. For this reason, it is possible to provide a superior active vibration blocking performance in low frequency bands when, for example, a vibration controlling operation or a vibration-eliminating operation is carried out.
In a conventional active vibration-eliminating device using a solid-state actuator such as a piezo-electric element, an actuator having a multiple laminated layers of solid-state elements has been used so as to gain a longer stroke of the solid-state actuator. For example, in a solid-state actuator using piezo elements, piezo elements of d33-type are laminated as high as 10 cm so as to provide a displacement of approximately 70 ìm. In contrast, in the present invention, when a displacement enlarging mechanism having a displacement enlarging rate of 10 times is used, it is possible to easily obtain an amount of distortion of 150 ìm by using laminated piezo elements having a length of 20 mm. This makes it possible to cut costs greatly and consequently to devote greatly to the promotion of active vibration control devices.
Moreover, the application of the displacement enlarging mechanism makes it possible to easily obtain a greater displacement so that the vibration control device can also be applied to the positional control and attitude control, which have not been realized without using an air actuator. Furthermore, in the case when a control target member is comparatively soft (in particular, when the rigidity of the supporting system supporting the actuator and the control target member is not sufficient), a vibration control device without a displacement enlarging mechanism has failed to carry out an appropriate controlling operation on the control target member since the displacement is absorbed by the deformation of the control target member. However, the above-mentioned displacement as much as 150 ìm is a sufficient size for carrying out an appropriate controlling operation even in such a case. Therefore, the range of application of the vibration control device using solid-state actuators can be expanded greatly.
Moreover, in the vibration control device in accordance with the above-mentioned aspect of the present invention, in addition to the displacement enlarging mechanism and the solid-state actuator, an inside elastic member is placed in series therewith so that the natural frequency of the vibration control device is reduced as compared with conventional devices; therefore, it is possible to obtain a superior passive vibration-blocking performance in high frequency bands. For example, on the assumption that the natural frequency of a vibration control device having no inside elastic member has a natural frequency of 10 to 20 Hz, when the inside elastic member is added thereto, the natural frequency of the vibration control device can be reduced to approximately 1 to 10 Hz.
In other words, in the vibration control device of this type, a soft support system (that is, the natural frequency is small) is provided independent of the size of the displacement (stroke) of the inside elastic member, which is a preferable characteristic for the passive vibration-eliminating system. It is assumed that the arrangement in which the inside elastic member is series-placed with the solid-state actuator and the displacement enlarging mechanism has not been adopted because a loss is generated due to the deformation of the inside elastic member; however, when a vibration isolating system is taken into consideration, the above-mentioned advantages exceed this disadvantage. This makes it possible to provide a vibration control system which sufficiently utilizes a small capacity of the solid-actuator, which is a major characteristic of a solid-actuator. For example, assuming that the displacement enlarging rate of the displacement enlarging mechanism is 10 times, and that the elastic constant of the inside elastic member is K, the supporting elastic constant of the second movable section is 0.1 K; thus, it is possible to easily obtain an elastic constant of {fraction (1/10)} of the inside elastic member. At this time, the controlling force of the solid-state actuator is reduced to {fraction (1/10)}, and taken out; however, in the case of microvibration, no problem arises even when the controlling force is small.
Moreover, one of the advantages of the application of a solid-state actuator is that an operation is available up to high frequency bands; and this characteristic is sufficiently exerted even in the arrangement like the vibration control device of the present embodiment, in which the inside elastic member is placed in series therewith. This is because the solid-state actuator is allowed to displace in proportion to the applied electric signal (current), and the application of an amplifier for supplying energy sufficiently up to high frequency bands makes it possible to obtain an output having a constant amplitude. On the assumption that this amplitude is x, in the case when the displacement enlarging rate of the displacement enlarging mechanism is 10 times and when the elastic constant of the inside elastic member is K, the action force outputted from the second movable section is 0.1 Kx, which indicates that a constant controlling force can be outputted up to high-frequency bands.
Moreover, in the vibration control device in accordance with the above-mentioned aspect of the present invention, since the inside elastic member is placed between the second movable section and the solid-state actuator in series therewith, an inside elastic member having a greater elastic coefficient with a smaller displacement (in other words, hard) can be used, as compared with a case in which the inside elastic member is placed on the side opposite to the first movable section with respect to the second movable section. For this reason, it is possible to reduce the volume of the inside elastic member, and consequently to miniaturize the vibration control device.
In the present invention, with respect to the inside elastic member, any known member, such as rubber and springs, may be used. More specifically, those members that are less susceptible to changes in the characteristics due to drifting and temperature changes (for example, a spring unit having a plurality of small coil springs aligned in parallel with each other, this unit molded by gel, a disc spring, etc.) may be preferably used.
Moreover, in the above-mentioned vibration control device, it is preferable to have an arrangement in which: the liquid displacement enlarging mechanism is provided with a liquid chamber in which liquid is sealed, the first movable section is allowed to contact the liquid inside the liquid chamber, and the second movable section is allowed to contact the liquid inside the liquid chamber with a contact area smaller than that of the first movable section. In other words, the liquid displacement enlarging mechanism is provided with the liquid chamber in which liquid is sealed, the first movable section, and the second movable section having a contact area to the liquid that is smaller than that of the first movable section, and a solid-state actuator is placed on the first movable section side (hereinafter, such a mechanism is referred to as xe2x80x9cliquid lever mechanismxe2x80x9d in the present specification).
In the liquid lever mechanism, a force transmission is made through liquid, and the resulting advantage is that the place and direction in which a force is exerted can be changed with high degree of freedom. This makes it possible to place the solid-state actuator in a place at which it is easily maintenanced, and the second movable section is placed in the vicinity of the control target member. Conventional devices have failed to realize this effect.
Moreover, in comparison with a mechanical displacement enlarging mechanism using, for example, a lever, the liquid lever mechanism has an advantage that it has hardly any high-order vibration modes in the degree of freedom in the non-rigidity internal structure.
With respect to the liquid inside the liquid chamber, it is preferable to use a non-volatile, stable liquid such as silicone oil; however, the present invention is not intended to be limited thereby. It is not necessary for the liquid itself to have a damping characteristic to vibration, and it is preferable to use a liquid having a high flowing characteristic with a small viscosity; that is, such a liquid exerts a superior rising property when controlled.
Moreover, a vibration control device in accordance with another aspect of the present invention is provided with: a displacement enlarging mechanism having a liquid chamber in which liquid is sealed and a number of small particles whose volume is elastically variable are dispersed, a first movable section that is allowed to contact the liquid inside the liquid chamber and a second movable section that is allowed to contact the liquid inside the liquid chamber with a contact area smaller than that of the first movable section; and a solid-state actuator which is placed on the side opposite to the second movable section with respect to the first movable section and which is displaced in a direction along which the first movable section of the displacement enlarging mechanism is shifted, based upon an electric signal supplied thereto.
Furthermore, a vibration control device in accordance with still another aspect of the present invention is provided with: a displacement enlarging mechanism having a gas chamber having a gas sealed therein, whose volume is elastically variable, a first movable section that is allowed to contact the gas inside the gas chamber, a second movable section that is allowed to contact the gas inside the liquid chamber with a contact area smaller than that of the first movable section; and a solid-state actuator which is placed on the side opposite to the second movable section with respect to the first movable section and which is displaced in a direction along which the first movable section of the displacement enlarging mechanism is shifted, based upon an electric signal supplied thereto.
In accordance with this vibration control device, the liquid lever mechanism (or the gas lever mechanism) makes it possible to enlarge the displacement of the solid-state actuator so that it provides a superior active vibration-blocking performance at low frequency bands, and also to reduce the natural frequency as compared with conventional devices so that it provides a superior passive vibration-blocking performance at high frequency bands. Moreover, a number of small particles whose volume is elastically variable are dispersed inside the liquid chamber (or the gas chamber whose volume is elastically variable is used) instead of the inside elastic member, and since these particles serve as the elastic member, it is not necessary to place another elastic member outside the liquid chamber (or the gas chamber), thereby making it possible to further miniaturize the vibration control device.
Moreover, the vibration control device of the present invention may be further provided with a mechanism for adjusting the pressure of the liquid chamber or the gas chamber. For example, a piston may be externally inserted into the liquid chamber so that the position of the second movable section is changed; and this means is convenient. In a conventional vibration control device having a solid-actuator, it is necessary to strictly carry out the positional adjustment on the solid-state actuator, and the adjustment in which a jack, etc. has to be used is comparatively difficult. In contrast, in the present invention, the adjustment of pressurization level to be applied to the solid-state actuator is easily carried out by changing the pressure inside the liquid chamber.
Moreover, in the vibration control device of the present invention, the peripheral portion of the first movable section may be sealed with the inside elastic member. It is important for the liquid lever to positively seal the first and second movable sections of the liquid chamber so as to prevent the liquid from leaking. By sealing the peripheral portion of the first movable section with the inside elastic member, it is possible to prevent leakage of the liquid with higher reliability, to reduce the number of parts and the number of manufacturing processes, and consequently to cut production costs.
Furthermore, in the vibration control device of the present invention, the inside elastic member may be placed inside the liquid chamber. With this arrangement, it is not necessary to place a separate inside elastic member outside the liquid chamber, and consequently to make the vibration control device more compact.
In the vibration control device of the present invention, the inside elastic member may be placed between the first movable section and the solid actuator. With this arrangement, since the inside elastic member is placed between the first movable section and the solid actuator, the inside elastic member is maintenanced more easily as compared with a case in which, for example, the inside elastic member is placed in the liquid chamber between the first movable section and the second movable section.
Moreover, in the vibration control device of the present invention, rigid members may be placed on both of the ends of the inside elastic member in the distortion direction. With this arrangement, since the rigid members are placed on both of the ends of the inside elastic member in the distortion direction, the displacement of the solid-state actuator locally placed may be transmitted to the displacement enlarging mechanism more efficiently.
In the vibration control device of the present invention, the displacement enlarging mechanism, the solid-state actuator and the inside elastic member may be assembled into one case. Thus, it is possible to further miniaturize the vibration control device.
The vibration control device of the present invention may be arranged so that the load applied to the solid-state actuator is controlled. Moreover, the vibration control device of the present invention may also be provided with an inside parallel elastic member placed in parallel with the solid actuator. With these arrangements, the load applied onto the solid actuator is controlled so that the solid actuator is optimally operated. In other words, when all the applied load is imposed on the solid actuator, the solid-state actuator is not operated at its operational best suited point. Therefore, in order to use each solid-state actuator at its best suited point, it is preferable to adjust the load, and the inside parallel elastic member is placed in parallel with the solid actuator so as to realize such an adjustment.
Moreover, in the vibration control device of the present invention, a coat member for coating the solid-state actuator may also be provided. Such a structure is realized by molding the solid-state actuator with an elastic material. Here, the solid-state actuator may be molded by the inside parallel elastic member so that it becomes possible to shield the solid-state actuator from influences of outside humidity, and consequently to ensure a long service life of the solid-state actuator.
In the vibration control device of the present invention, the peripheral portions of the first and second movable sections may be sealed with elastic members. It is important for the liquid lever mechanism and gas lever mechanism to positively seal the first and second movable sections of the liquid chamber or the gas chamber so as to prevent the liquid or gas from leaking. Since the vibration control device of the present invention is mainly used for controlling microvibration, the application of the elastic seal members makes it possible to prevent leakage of the liquid or gas with higher reliability. With respect to the elastic seal member, for example, an O-ring or X-ring may be used.
The vibration control device of the present invention may also be provided with a cushion elastic member placed on the side opposite to the first movable section with respect to the second movable section. With this arrangement, in the case when a shearing force is externally applied in a direction orthogonal to the shifting direction of the second movable section, the cushion elastic member functions as a cushion member (in other words, a member for releasing the shearing force) for the shearing force, thereby making it possible to prevent damages to the second movable section.
In the vibration control device of the present invention, the cushion elastic member may be placed in series with as well as in parallel with the second movable section. With this arrangement, it becomes possible to adjust the force imposed on the second movable section, and also to control the force applied to the solid-actuator. In other words, it is possible to reduce the load imposed on the second movable section, and consequently to allow the second movable section to share only the controlling force. The cushion elastic member, parallel-aligned in this manner, is allowed to distort only in the displacement direction of the second movable section, and consequently to generate an elastic force. Moreover, the control efficiency is allowed to increase as the vibration damping in the cushion elastic member parallel-aligned decreases.
Moreover, in the vibration control device of the present invention, the cushion elastic member may have a portion formed by alternately laminating at lease either of steel plates and resin plates, and elastomer. Such an elastic member formed by alternately laminating at lease either of steel plates and resin plates, and elastomer (hereinafter, referred to as xe2x80x9cnon-interference elastic memberxe2x80x9d) functions desirably as a cushion member for the shearing force.
The vibration control device of the present invention may have an arrangement in which a plurality of the solid-state actuators are placed in parallel with each other. This arrangement makes it possible to generate a greater operational force.
Moreover, the vibration control device of the present invention may have an arrangement in which a plurality of the second movable sections are placed in parallel with each other with respect to the single displacement enlarging mechanism. With this arrangement, a plurality of the second movable sections can be simultaneously operated by using the single displacement enlarging mechanism, so that, for example, an object to be subjected to the operational force can be driven stably, or the operational force may be applied to two different objects simultaneously.
The vibration control device of the present invention may have an arrangement in which a plurality of the first movable sections and solid-state actuators are respectively placed on both of the ends of the displacement enlarging mechanism in a manner so as to face each other. With this arrangement, a portion of the operational force released outside is reduced, with the result that the operational force is transmitted to the second movable section at a higher rate. This arrangement is particularly effective, when applied to a vibration control device that is provided with the displacement enlarging mechanism having the liquid chamber having a number of small particles whose volume is elastically variable dispersed therein or the displacement enlarging mechanism having the gas chamber whose volume is elastically variable. Moreover, this arrangement allows a comparatively great number of piezo-actuators to be placed within a narrow flat area so that a greater operational force can be obtained.
Moreover, the vibration control device of the present invention may be further provided with a sensor for measuring the distance from a control target member placed on the side opposite to the first movable section with respect to the second movable section. With this arrangement, the position and orientation (that is, attitude) of the control target member can be controlled accurately by using the solid-state actuator.
Furthermore, in the vibration control device of the present invention, the solid-state actuator may include a piezo-element or the solid-state actuator may include a super-magnetostrictive element. In particular, the solid-state actuator including the super-magnetostrictive element is advantageous in that it provides a greater displacement and is less susceptible to damages.
With respect to a driving operation of the vibration control device, it is preferable to provide an arrangement in which: a vibration signal of a control target member is measured based upon the displacement of the second movable section, based upon the vibration signal, a driving signal is generated so as to allow the control target member to cause predetermined vibration (or to regulate the control target member from generating vibration), and the solid-state actuator is driven by the driving signal.
In this case, it is preferable to provide a controlling process in which: the relative displacement of the control target member is detected so that the relative positional error from the target position of the control target member is found, and an electric signal to be supplied to the solid-state actuator is controlled so as to allow the control target member to trace the target position. Such a driving method makes it possible to properly operate the device so as to allow the control target member to generate vibration or to regulate it from generating vibration. Moreover, a voltage supply may be cut off from any of the solid-state actuators that has been damaged, thereby making it possible to realize a driving operation with reduced power consumption. This arrangement may be achieved by incorporating a fusing mechanism in the controlling circuit of the solid-state actuator and disconnecting the corresponding fuse so as to cut off the power supply to the damaged solid state actuator.
Here, an explanation will be given of a specific application of the vibration control device of the present invention. In recent years, precision apparatuses tend to have degradation in their precision or a reduction in their productivity due to influences of microvibration caused by the installation environment; therefore, in order to prevent these influences, active vibration-eliminating devices having a solid-state actuator such as a piezo-element have been used. The active vibration-eliminating device actively controls floor vibration so as to reduce the vibration, and also has a reducing function with respect to vibration that the device itself generates. In general, the controlling operation of the active vibration-eliminating device is carried out with three-dimensional, six degrees of freedom, and a plurality of solid-state actuators, which are aligned in directions orthogonal to each other, have been used. With respect to actuators for active vibration-eliminating device that have been developed for this purpose, air pressure elements, linear motors, piezo-elements and super-magnetostrictive elements have been put into practical use. The present invention makes it possible to achieve high-performance active vibration-eliminating devices.
Moreover, microvibration applying bases which enable simulating operations for microvibration have been developed; and the vibration control device of the present invention, which enables both of the vibration-eliminating and vibration-generating operations within a wide frequency range, is best suited for the application to these microvibration applying bases. Moreover, active vibration-suppressing devices in which a mass body is allowed to vibrate and the reactive force is utilized for reducing vibration have been put into practical use; and the vibration control device is also best suited for this field.
Moreover, a vibration control device in accordance with another aspect of the present invention has an arrangement in which a plurality of the above-mentioned displacement enlarging mechanisms are installed.
With this arrangement, since a plurality of the displacement enlarging mechanisms are placed in series with each other so that a displacement in each displacement enlarging mechanism is enlarged to a multiple of the predetermined value; that is, a comparatively small displacement caused by one solid-state actuator is inputted to the first movable section at the initial stage so that a great displacement is outputted from the second movable section at the final stage of the displacement enlarging mechanism. Therefore, the vibration control device can be utilized for applications that require a particularly large displacement, such as a positional control operation and an attitude control operation. Furthermore, even in the case when a control target member is a comparatively soft member, it can provide a suitable controlling operation on even such a control target member. Thus, it becomes possible to greatly widen the scope of applications of the vibration control device using a solid-state actuator.
Moreover, the inside elastic member, placed in series therewith, makes it possible to reduce the natural frequency of the vibration control device as compared with conventional devices, and consequently to simultaneously obtain the above-mentioned advantage, that is, the superior passive vibration-blocking performance at high frequency bands.
Furthermore, in the case when the displacement of the solid-state actuator is enlarged by using, instead of the inside elastic member, the liquid lever mechanism (or the air lever mechanism having a gas chamber whose volume is elastically variable) in which a number of small particles whose volume is elastically variable are dispersed, it is not necessary to place another elastic member outside the liquid chamber (or the gas chamber); thus, it is possible to obtain a small-size vibration control device suitable for passive vibration-eliminating process.
Moreover, a vibration control device in accordance with still another aspect of the present invention is provided with a plurality of the displacement enlarging mechanisms respectively aligned in series with each other, each having the first and second movable sections, with a displacement inputted to the first movable section being enlarged and outputted from the second movable section, and a solid-state actuator that is placed on the side opposite to the rest of the first and second movable sections with respect to the first movable section located at the leading portion of the displacement enlarging mechanisms placed in series with each other, and that is displaced in a direction along which the first movable section located at the leading portion of the displacement enlarging mechanisms is moved, in accordance with an electric signal supplied thereto.
Moreover, in a vibration controlling structure of the present invention, a plurality of the vibration control devices are combinedly used for one or a plurality of members, with their operation directions, caused by displacements of the second movable sections, being aligned orthogonal to each other.
In this structure, a plurality of the vibration control devices are combinedly used for one or a plurality of members, with their operation directions, caused by displacements of the second movable sections, being aligned orthogonal to each other; therefore, it is possible to carry out a vibration controlling operation with multiple-dimensional, multiple-degrees of freedom. Moreover, the elastic members, placed in series therewith (or, instead of the inside elastic members, a number of small particles whose volume is elastically variable, dispersed in the liquid chamber, or a gas chamber whose volume is elastically variable), make it possible to reduce the natural frequency of the vibration control device as compared with conventional devices, and consequently to obtain a superior possible vibration-blocking performance at high-frequency bands. Here, in the present invention, xe2x80x9cseriesxe2x80x9d refers to a state in which an interaction of forces is carried out in series with each other, and it does not refer to a mechanical linear alignment.
Other features and advantages of the present invention will be apparent from the following description taken in connection with the accompanying drawings.